rubocop: enable Style/IfUnlessModifier.

Library/.rubocop_shared.yml

Library/Homebrew/.rubocop.yml

Library/Homebrew/brew.rb

Library/Homebrew/cask/artifact/abstract_uninstall.rb

Library/Homebrew/cask/artifact/artifact.rb

Library/Homebrew/cask/artifact/installer.rb

Library/Homebrew/cask/artifact/pkg.rb

Library/Homebrew/cask/artifact/stage_only.rb

Library/Homebrew/cask/audit.rb

Library/Homebrew/cask/cask_loader.rb

Library/Homebrew/cask/dsl.rb

Library/Homebrew/cask/installer.rb

Library/Homebrew/cask/metadata.rb

Library/Homebrew/caveats.rb

Library/Homebrew/cleaner.rb

Library/Homebrew/cleanup.rb

Library/Homebrew/cli_parser.rb

Library/Homebrew/cmd/deps.rb

Library/Homebrew/cmd/gist-logs.rb

Library/Homebrew/cmd/info.rb